The present invention relates to tappets for use in internal combustion engines, to transmit motion directly from a cam lobe profile of an engine cam shaft to an engine poppet valve. Thus, the present invention relates to engine valvetrain of the “direct acting” type.
Although the improved tappet of the present invention could be utilized in various types of engines, in terms of the type of fuel utilized by the engine, the present invention is especially advantageous when used in a gasoline engine with Port Fuel Injection of the type utilizing intake valve deactivation for one of a pair of intake poppet valves. The invention is even more advantageous in an engine valve control system of the type described above which is utilized for “swirl” control, as that term is now well understood by those skilled in the engine art.
In terms of the type of lift imparted to the engine poppet valve in a direct acting valve train, there are two general categories of such tappets. The first is the conventional mechanical or hydraulic tappet (“bucket tappet”) which receives its input from a single cam lobe profile and therefore, imparts only a single “valve event” to the engine poppet valve. The second category comprises “dual lift” tappets of the general type illustrated and described in U.S. Pat. No. 5,193,496. In dual lift tappets of the type taught in the '496 patent, the tappet includes a central portion and an outer portion with the central portion engaging a low lift cam, to produce a low lift valve event, and the outer portion of the tappet engaging a pair of high lift cam lobe profiles to provide a high lift valve event. Thus, the known, prior art dual lift direct acting tappet typically has associated therewith three separate cam lobe profiles (one low lift, and two high lift), making such an arrangement extremely expensive to manufacture and difficult to package.
The improved tappet, and improved valve control system of the present invention was developed in connection with an effort to improve what is referred to as the “charge motion” (i.e., the flow pattern of the air-fuel mixture after it flows past the intake poppet valve). Specifically, the effort was to increase the charge motion at low to medium engine speeds, on gasoline engines utilizing port fuel injection. It was believed that a dual lift tappet arrangement was needed for this particular application, although for the reasons discussed previously, it was clearly not acceptable to require three, or even two, separate cam lobe profiles for each intake poppet valve, merely to achieve the desired dual lift valve event for each intake poppet valve.
It was also determined during the course of development of the present invention that for this particular type of engine application, utilizing port fuel injection, it would not be acceptable for the dual lift tappet to provide, selectively, either a normal lift (“high lift”) valve event, or a deactivated valve event. During the low speed operation of the engine, with one of the two intake poppet valves deactivated, it was observed that because of the fuel being injected directly into the intake port, a quantity of fuel would accumulate behind the deactivated valve, over a period of time. Then, once that particular intake poppet valve would again be operated in the normal lift mode, the quantity of fuel which had accumulated would be drawn into the combustion chamber, and could result in an uncontrolled combustion condition. Such an uncontrolled combustion condition could lead to various operating problems of the engine, such as extra, undesirable emissions and NVH (“noise-vibration-harshness”) type conditions.